This invention relates to improvements in a gas chromatographic detector having an RF powered plasma giving off light that is analyzed by emission spectroscopy as reported by McCormack, Tong and Cooke in Analytical Chemistry, 1965, 37, 1470. In their detector, gas containing the chemical compounds to be analayzed is passed through a discharge contained within a tube mounted within the resonant microwave cavity that, because of cost considerations, is powered by the magnetron used in microwave ovens for the home. The microwave powered discharge in the discharge tube breaks the molecules of the gas into atoms. The discharge excites the atoms so that characteristic spectral emission of the atoms is given off.
Inasmuch as the problem of tailing has generally been the fault of the column employed and not the fault of the detector, it has been presumed that the tailing usually present when an automatic emission detector was used was also due to the column. We have discovered, however, that an error of as much as 5% has been due to tailing caused by the detector itself and that this is due to the fact that the inner walls of the discharge tube run at a very high temperature. Furthermore, the high temperature causes rapid degradation of the discharge tube so that it must be replaced often. Because of its location, replacement of a discharge tube can take a few hours during which the detector can be out of service. Whereas these problems can be partially overcome by reducing the radio frequency power employed, this degrades the sensitivity of the detector.